1. Field of the Invention
The present invention relates to a machine shop tool and associated method for determining the deviation of dimensions between objects and, more particularly, the deviation in length between two points on a reference object and two points on a workpiece.
2. Background Information
It is well known that some of the items manufactured by machine shops are precisely machined metal objects. Frequently, such metal objects must have dimensions that are machined to tolerances of several thousandths of an inch. It is necessary to have gauges that can measure such close tolerances to provide the required precision machining of the objects.
One common way of measuring tolerances is through the use of well known dial calipers. One drawback in using dial calipers, however, is that they are not capable of measuring shallow grooves, such as O-ring grooves, that may be as shallow as 0.020 of an inch and as narrow as 0.050 of an inch, or short turn bores that may be as shallow as 0.020 of an inch, that are machined in metal workpieces. That is because the anvils of the dial calipers that must be physically positioned within the O-ring groove or short turn bore are too large to fit within the groove or bore. Therefore, if a dimension of an object cannot be measured with dial calipers, the dimension must be measured with some other device that is capable of taking the measurement, such a well known height set machine. However, since height set machines are not readily portable, the workpiece must be transported from the work location to the height set machine for the measurement.
Other known devices, for measuring precise tolerances of dimensions include micrometers and telescoping bore gauges. These devices, likewise, are not capable of measuring shallow grooves or short turn bores because of the large dimensions of members that must fit within the groove or bore.
Further, most of these gauges provide only absolute readouts of the actual distance between two points on an object and cannot provide a direct readout that is a comparison of the relative distance between a pair of points on each of two different objects. Such comparison measuring is extremely useful if a particular object is machined, through trial and error, to a particular shape having acceptable dimensions and that object is then to be used a reference for reproducing similar objects, or workpieces, with the same dimensions. Also, such comparison measuring is useful if the distance between two points on a workpiece is to be compared with a standard reference distance, such as the distance between two points on a standard gauge block. A number of devices have been proposed for measuring absolute distances between two points on objects.
U.S. Pat. No. 443,869 discloses a micrometer gauge having a body member with a fixed stop and a ruler-like slideable member having movable stop that moves with the slide. The slide includes a plurality of markings that are representative of the distance between the movable stop and the fixed stop. Also included is a dial with a needle that rotates one complete turn for each unit of distance that the slide is moved out from the body member. The dial has a plurality of markings that correspond to fractions of units on the slide. When the slide is slid relative to the body member, the slide indicates the number of integral units of lengths between the fixed stop and the movable stop while the dial indicates the additional fractional units of length between the fixed stop and the movable stop. In use, the fixed stop and the movable stop are positioned against two points on the object to be measured. The length between the two points may then be determined by adding the integral number of units of length shown on the sliding scale to the fractional portions of a unit shown in the rotating indicator. This gauge is for measuring absolute distances and not for directly comparing one distance to another. Also, the stops are of such a relatively large size that they cannot be positioned in small areas such as is necessary when measuring an O-ring groove or a short turn bore.
U.S. Pat. No. 1,065,744 discloses a micrometer gauge having a movable stop, a fixed stop, a dial having a rotatable indicator and a worm gear for rotating the indicator and moving the movable stop relative to the fixed stop. Two points on an object to be measured are positioned, respectively, adjacent the movable stop and the fixed stop. The worm gear is then rotated until the movable stop and the fixed stop come in contact with the two points on the object. The worm gear also rotates the indicator to a position on the dial that corresponds to the distance between the two points. Again, this gauge provides only an absolute measurement of the distance between two points on an object rather than a direct comparison between the lengths of two different objects. Also, the stops are of such a relatively large size that they cannot be positioned in small areas such as is necessary when measuring an O-ring groove or a short turn bore.
U.S. Pat. No. 3,054,189 discloses an adapter for a dial indicator gauge. The adaptor includes apparatus for holding a standard dial indicator in a fixed position relative to a stop member. A movable arm, of the indicator, is positioned against a movable member that supports a movable stop. The movable and fixed stops are placed against two points on an object to be measured. Movement of the movable stop, when it is placed in contact with the object, moves the arm of the indicator which, in turn, causes the dial to display the distance between the two points on the object. Again, this device makes absolute measurements of distance between points on objects rather than a comparison of the relative distances between pairs of points on two different objects. Also, the stops are of such a relatively large size that they cannot be positioned in small areas such as is necessary when measuring an O-ring groove or short turn bore.
U.S. Pat. No. 4,291,465 discloses a caliper rule device having an extended measurement range. The device includes a body member and a sliding member that is attached to a dial scale. The sliding member has a movable stop while the body member has a fixed stop that may be positioned in any one of a plurality of fixed locations on the body member. The fixed locations on the body member are separated by predetermined units of length. The fixed and movable stop are placed, respectively, in contact with two points on an object between which a distance is to be measured. The distance is then equal to the sum of the reading on the dial and the distance between the end of the body member that is adjacent the sliding member and the fixed stop. Again, this device is for measuring absolute distances and not for comparing dimensions between two different objects. Also, the stops are of such a relatively large size that they cannot be positioned in small areas such as is necessary when measuring an O-ring groove or a short turn bore.
Therefore, a need exists for a gauge that is capable of providing an indication of a comparison of the distance between two points on one object, such as a reference object, and the distance between two points on a second object, such as a workpiece. Further, a need exists for a gauge that is dimensioned so that it can be employed when measuring shallow grooves, such as an O-ring groove, or a short turn bore. Additionally, a need exists for a gauge that is readily portable and can be easily transported to and used at a workstation. The present invention provides a solution to these needs.